Modern mobile communications are leaning more and more towards offering the user multimedia services with high speed transmission. FIG. 1 illustrates a system architecture of System Architecture Evolution (SAE).
Amongst the system, user equipment (UE) 101 is a terminal device used to receive data. Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102 is a wireless access network, wherein, the UE includes a wireless network interface that provides access to a macro base station (eNodeB/NodeB). Mobile Management Entity (MME) 103 is responsible for managing mobile context, session context, and security information of UE. Service Gateway (SGW) 104 primarily provides user plane function. MME 103 and SGW 104 can exist within the same physical entity. Packet Data Network Gateway (PGW) 105 is responsible for billing and legitimate interception functions, and can also be located in the same physical entity as SGW 104. Policy and charging rules function entity (PCRF) 106 provides Quality of Service (QoS) policy and billing standards. Service General Packet Radio Service (GPRS) Support Node (SGSN) 108 is a network node device that provides routing for data transmission in a Universal Mobile Telecommunications Service (UMTS). Home Subscriber Service (HSS) 109 is the UE s home attribution subsystem responsible for protection on user information, including the current location of the user equipment, service node address, user security information, a packet data context of the user equipment, etc.
In release 12 (Rel-12), 3GPP raised the demand for small cell enhancement. Target scenarios of the small cell enhancement include macro cell coverage scenarios as well as scenarios without macro cell coverage, indoors and outdoors, and ideal and non-ideal backhaul enhancement, as shown in FIG. 2.
Under circumstances where there is macro cell coverage, it is proposed that carrier aggregation technology can be used between different base stations. Macro cells and small cells can work at different bands. There are many kinds of architecture for technology using different carrier aggregations between base stations, such as, radio access network RAN split based UP architecture and core network split based UP architecture. A CN split based architecture refers to that data are sent directly to Pico by the core network SGW for those bearers in pico cell, User plane data is not forwarded through macro cells. In small cell architecture, another possible type of architecture has an S1GW or small cell GW between the base station and the core network. The base station interacts with the CN through the S1GW.
In regards to a user plane architecture based on core network split, every time the second base station SeNB changes, there is signaling exchange through a core network. In a scenario without macro cell coverage, every time the switch between pico base stations occurs, it must go through a CN signaling exchange. Since the range of pico or SeNB coverage is comparatively small, this type of frequent signaling exchange with CN creates a burden on the core network.
In order to reduce the signaling exchange with the CN, it is possible to terminate the bearer switch between different base stations, e.g., the switch from SeNB1 to SeNB2, at S1GW. However, current security mechanisms do not support switch process termination at the gateway.
Following is a simple introduction to the current security mechanism.
Security levels in E-UTRAN are shown in FIG. 3.
K exists in a permanent key on an Authentication Center (AuC) on a universal integrated circuit card on a universal subscriber identity module (USIM).
CK and IK are a pair of keys created by AuC and USIM in an AKA (authentication and key agreement) process. CK and IK processes are not the same in the security context of evolved packet service (EPS) and that of legacy.
Kasme is a key created between the UE and MME after AKA concludes. UE and MME then further create keys for NAS layer encryption (KNASenc) and integrity protection (KNASint) based on Kasme.
KeNB is a key derived from ME and MME, or from ME and eNB.
NH is a key created by ME and MME for forward security.
Based on KeNB, an air interface access layer user plane encrypted key KUPenc, a control plane encrypted key KRRCenc, and a control plan integrity protection key KRRCint are further derived.
The theory of key generation at switch is shown in FIG. 4. The initial KeNB is calculated based on Kasme and NAS uplink count. When UE and eNB need to setup an initial access stratum (AS) security context, MME and UE derive KeNB and NH. KeNB and NH are derived based on Kasme. NCC has a relation to every KeNB and NH. Every KeNB has a relation to the NCC corresponding to the NH that the KeNB is derived from. At start up, KeNB is immediately derived from Kasme so KeNB is associated with a virtual NH, which is 0 in respect to NCC. During initial setup, the derived NH and NCC1 are associated. When eNB receives an initial context setup request, NCC is initialized as 0.